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Cathode Follower SET Amp [message #11403] Fri, 02 November 2007 04:28 Go to next message
FredT is currently offline  FredT
Messages: 704
Registered: May 2009
Illuminati (1st Degree)
Here's an interesting new design.

Re: Cathode Follower SET Amp [message #11404 is a reply to message #11403] Fri, 02 November 2007 10:03 Go to previous messageGo to next message
SteveBrown is currently offline  SteveBrown
Messages: 330
Registered: May 2009
Grand Master
Fred, it does look interesting, but I wish manufacturers would stay away from satements like this: "Traditional single-ended amplifiers have little bass drive below 100 Hz." What?? Of course, I guess if we're using "traditional" to mean an original WE 91 amp, maybe that's true. Anyway, would be an interesting little amp to audition.

Re: Cathode Follower SET Amp [message #11405 is a reply to message #11404] Fri, 02 November 2007 10:11 Go to previous messageGo to next message
real_one is currently offline  real_one
Messages: 55
Registered: May 2009
Baron
I agree. That's a blanket statement that doesn't consider iron or wiring (parafeed, transformer coupled, etc.) I know that's a commercial site but it still bothers me to see marketing blather.

Re: Cathode Follower SET Amp [message #11411 is a reply to message #11405] Thu, 08 November 2007 13:12 Go to previous messageGo to next message
Thermionic is currently offline  Thermionic
Messages: 208
Registered: May 2009
Master
Indeed. Depending on the low frequency cutoff points throughout the amp, and the output transformer design and its reflected impedance ratio, a SE amp can reach flat to below 40Hz.

What the manufacturer doesn't mention is the one great inherit drawback of cathode follower output stages. Cathode followers have less than unity gain, so 100% of the voltage swing must come exclusively from the small signal stages. Most any small signal stage's distortion spectrum will be weighted heavier towards high order harmonics than a DHT power triode using a "traditional" output transformer output coupled configuration. This is especially true for cascode stages, and other super high gain small signal stages capable of such large voltage swings. Even a voltage amplifier stage using highly linear, low mu small signal triodes cascaded together won't be low distortion any longer by the time it has to swing a few hundred volts. There's a good reason why cathode follower output stages aren't more popular.

Thermionic

Re: Cathode Follower SET Amp [message #60485 is a reply to message #11411] Tue, 28 July 2009 17:19 Go to previous message
SASAudioLabs is currently offline  SASAudioLabs
Messages: 17
Registered: May 2009
Chancellor
Thermionic wrote on Thu, 08 November 2007 13:12

Indeed. Depending on the low frequency cutoff points throughout the amp, and the output transformer design and its reflected impedance ratio, a SE amp can reach flat to below 40Hz.

What the manufacturer doesn't mention is the one great inherit drawback of cathode follower output stages. Cathode followers have less than unity gain, so 100% of the voltage swing must come exclusively from the small signal stages. Most any small signal stage's distortion spectrum will be weighted heavier towards high order harmonics than a DHT power triode using a "traditional" output transformer output coupled configuration. This is especially true for cascode stages, and other super high gain small signal stages capable of such large voltage swings. Even a voltage amplifier stage using highly linear, low mu small signal triodes cascaded together won't be low distortion any longer by the time it has to swing a few hundred volts. There's a good reason why cathode follower output stages aren't more popular.

Thermionic http://www.audioroundtable.com/emoticons/smiley.gif


I absolutely concur with Thermonic and back him completely.

Take care.
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